1. Field of the Invention
This invention relates to water wells and more particularly to a process of developing or cleaning a well and rejuvenating a well.
2. Description of the Prior Art
After drilling a water well, some water will flow into the well from the aquifer (the water bearing formation or strata). If the aquifer is sandy so that the sand of the formation tends to flow into the well, it is necessary to place casing in the well to hold back the sand of the aquifer. The casing at the aquifer is formed into a screen by slitting the casing with narrow slits. If the slits are made wide, the sand itself will flow into the casing, defeating the purpose of the casing. Therefore, often the slits in the casing at the screen are quite narrow and the slits themselves will only be for one to five percent of the total area of the casing. Often after the casing is placed in the well and before water production or development of the well, the well is gravel packed, i.e., a filter bed of gravel is placed between the casing and the well bore.
After the well is cased and gravel packed, the well is developed. As used herein, the word "developed" means the process performed on a new well by which the mud cake formed by drilling is removed and fines and silt within the aquifer are washed from the aquifer to increase the water flow into the casing.
Pumping water from the well itself is one type of development. With the pumping of the water, certain of the fines and silt will flow from the aquifer whether or not the well is gravel packed. Also, of course, a sufficient flow of water will even bring some of the mud cake from the walls. Accompanied by pumping the well, the well may be backwashed, which is to say that water is pumped from the well and then the ceased and the water in the eduction tube is permitted to gush back into the well, causing a certain amount of agitation which stirs up the fine material to be removed from the well. Because of the sand removed, development by pumping and backwashing caused wear on the pump.
Another type of development is high-speed bailing. By these procedures, a bailer or bucket on a cable is lowered to the bottom of the well and reeled upward at high speed. The movement of the bailer within the casing will cause a high pressure above the bailer and a low pressure or vacuum below the bailer. This, itself, will agitate the material around the well to remove undesired material therefrom.
In addition to the above, it has been suggested that one could develop a well by high velocity water jets. Specifically, "Ground Water and Wells," First Edition 1966, published by Edward E. Johnson, Inc., St. Paul, Minn. Page 309 thereof states that the water may be jetted against the screen at a velocity of 190 feet per second and a pressure of 250 psi and having a discharge 104 gallons per minute. On Page 389, "Ground Water and Wells," it is stated that it is desirable to use an air lift accompanying the jetting.
Also, "Water Well Manual," by V. P. Gibson and R. D. Singer, Premier Press, Berkely, California, 1969, 3rd printing 1973, beginning on Page 101, describes such a high velocity jetting. They describe the process using water at 100 psi and 10 gallons per minute per each 3/16th inch nozzle used in jetting water. It is also suggested in "Water Well Manual" to accompany the action with pumping the well.
E. W. Denison in "Ground Water--Its Development, Use and Conservation," published by Edward E. Johnson, Inc., St. Paul, Minn., First Edition 1947, at Page 237, describes what is called "Air Development of Wells." In it an air lift or pump is used. I.e., an air pressure hose is lowered into the well and the end of the hose is within the bottom of the eduction tube. Of course, it is recognized that if as much as 30% of the eduction tube from the bottom of the well to the top of the ground is standing under water, putting air into the eduction tube at the bottom will cause water to flow to the top. Then, a regular flow of air will cause the well to pump. However, if the air valve is opened wide, there will be a surge of air which will blow out from the eduction tube and around the screen and into the formation. This process is described on Page 237 and the desirable pressures to be used are said to be 100 to 150 psi. I can find no reference to using air pressures higher 150 psi.
In "Ground Water and Wells," cited above, the description of air development is found on Page 303 and following pages. Again, the preferred pressures are listed as 100 psi to 150 psi. It is stated that for the expected production of the well there should be 3/4 cubic foot of air available for each gallon of water. I.e., if the well was expected to product 100 gallons per minute of water, there should be 75 cubic feet per minute of air available. On Page 304, he gives a specific example that with a well expected to produce 400 to 700 gallons per minute of water, a 10 inch or larger casing would be used and an 8 inch eduction tube would be used and a 2.5 inch air pipe would be used. He indicates for optimum performance, there should be 60% submergence, i.e., 60% of the eduction tube should be below the water level, but the process will still operate with 30% submergence.
In old wells, i.e., wells which have been producing water for five or 10 years or more, often the production is reduced because the openings in the screen of the casing are decreased. The rusting of the casing itself may reduce the openings. Further, the slots may be closed, not only with gravel, but with silt, sand and fine material from extended use. Also, the screen may be clogged with algae. Various procedures have been developed for opening the screen, namely, acid or physically scraping with brushes or scrapers. Another means of cleaning or rejuvenating an old well is to detonate small charges of an explosive at the screen in the casing.
Before filing this patent application, a preliminary search disclosed the following U.S. Pat. Nos.;
Strumpf, 1,360,053; Yarbrough, 1,916,875; Hillger, 2,662,486; Beckett, 3,062,290; Edwards, 3,334,697; Dendy, 3,561,534; Peevey, 3,760,878.